The present invention relates generally to surgical instruments for occluding a vessel. More particularly, the invention relates to surgical instruments such as surgical clamps and other occlusion devices, and to replaceable clamp pads for attachment to such instruments, that provide for improved atraumatic occlusion of such vessels.
Instruments for occluding blood vessels during surgery, such as conventional metal or rigid surgical clamps or clips, are well known. However, such instruments are known to cause trauma to the clamped vessel at the clamping site. A number of atraumatic instruments have been developed for reducing or eliminating the trauma to a vessel during occlusion of the vessel. U.S. Pat. No. 3,993,076 to Fogarty, et al. describes a device whereby a vessel is occluded by using a resilient tape to press a vessel against a resilient pad. However, this device suffers from the disadvantage that it slips easily and can be cumbersome to use. For example, the pulsations of an occluded artery can tend to force the device off of its clamped position on the occluded artery. Conventional surgical clamps have also been adapted to include jaw surfaces containing resilient members or pads. These devices likewise are prone to slipping off of the clamped vessel. This can be especially problematic in situations where, due to obstructions, a vessel has been clamped with only the distal tips of the clamp jaws. In such situations, the vessel can be especially prone to slipping in the direction of the distal tips.
Of particular difficulty in preventing slippage of an engaged clamp along a clamped vessel is the nature of blood vessels themselves. Blood vessels generally consist of an inner endothelial layer, an intermediate layer of smooth muscle, and an outer layer of adventitia that is composed primarily of fibrous connective tissue. The connective tissue in the adventitia itself is organized into a series of layers with the innermost layer having denser, more closely packed connective tissue and outer layers gradually becoming looser and less densely packed. These outermost layers of adventitia under sufficient force or pressure can move relative to inner vessel layers, much like the movement of an outer sleeve over an inner sleeve. As a result, a surgical clamp engaged with and contacting the outer adventitial layer can slip along the vessel by virtue of the movement of the engaged outer adventitial relative to the inner layers. With increased clamping force, such slippage can be minimized but such additional force often leads to trauma to the vessel itself.
Other attempts have been made to atraumatically occlude a vessel in a secure fashion. U.S. Pat. No. 3,746,002 to Haller describes a vascular clamp with resilient gripping members located on the jaws. A plurality of pin members are embedded within the gripping members, the pin members of a length such that when a vessel is clamped between the members, the resilient material deflects to accommodate the vessel, exposing the pin members which grippingly engage the outer layer of the vessel, thus securing the vessel to the gripping member. While the Haller device is less traumatic to a vessel than other occlusion devices, it nevertheless has the disadvantage of traumatizing the outer layer of the vessel, as the pins are rigid and non-conforming to the vessel.
U.S. Pat. No. 4,821,719 to Fogarty describes a vascular clamp device containing resilient pads with Velcro-like hooks. The hooks interact with the external adventitial layer of the vessel forming a cohesive-adhesive relationship with the vessel similar to the bonding of Velcro materials. While this device offers a less traumatic way to occlude a vessel, the cohesive-adhesive nature of the bond can result in the removal of some of the adventitial layer of the vessel when disengaging the device. Also, slippage can still occur between the engaged adventitia and the inner vessel layers. Applied Medical (Laguna Hills, Calif.) manufactures a clamp pad under the tradename A-TRAC that contains a mesh surface layered over a soft cushion.
Still other efforts have been made to provide improved clamping of vessels while resisting movement. Our own U.S. application Ser. No. 08/993,076, filed Dec. 18, 1997, describes surgical clamps with resilient filaments extending from gripping surfaces. The filaments terminate in free distal ends that abut against the engaged vessel to restrict movement relative to the filament orientation. PCT International Publication No. WO 98/33437 describes other methods of increasing the traction force applied to a clamped vessel, including the use of bristles that axially crumple to develop an occlusive force and that resist movement of the vessel relative to the instrument. The column strength of each bristle provides traction in a predetermined direction.
Despite these advances, there remains a need for a surgical clamp having clamping pads or regions which atraumatically occlude vessels while avoiding the disadvantages previously associated with existing surgical clamps or occlusion devices, including pads that miminize slippage that occurs as a result of the relative movement between outer adventitia and inner vessel layers.